Polyalkylene oxides prepared by ring-opening polymerization of monoepoxides such as alkylene oxides with initiators have been commonly used as raw materials for sealing materials, adhesives and the like because such polyalkylene oxides are liquid at room temperature and after being cured, remain flexible even at comparatively low temperatures. For example, polyalkylene oxides used for sealing materials and adhesives are moisture-curing compounds having hydrolyzable silicon group(s) at end(s) (see, for example, Patent Documents 1 and 2).
Polyalkylene oxides are synthesized from initiators having active hydrogen group(s) such as hydroxy group(s) at end(s) which are polymerized in the presence of catalysts such as alkali metal catalysts, metal porphyrin catalysts, double metal cyanide complex catalysts, and P═N bond-containing compound catalysts. Particularly, the double metal cyanide complex catalysts are commonly used for the production of polyalkylene oxides, especially in the case that propylene oxide is used as an alkylene oxide. This is because the use of such double metal cyanide complex catalysts reduces the production of unsaturated mono-ols as by-products of polymerization and therefore results in the production of polyalkylene oxides having a high molecular weight and a narrow molecular weight distribution, which cannot be produced by alkali metal catalysts.
When a double metal cyanide complex catalyst is used for the production of polyalkylene oxides, the polymerization activity of the double metal cyanide complex catalyst should be activated by heating a certain amount of an alkylene oxide together with an initiator in the presence of the double metal cyanide complex catalyst. In the context of the present description, the step including heating in the presence of a certain amount of an alkylene oxide is referred to as a “batch reaction”. On the other hand, a step including continuously supplying an alkylene oxide is differently referred to as an “adding reaction”. Hereinafter, the step of activating the polymerization activity of a double metal cyanide complex catalyst is referred to as “activation of the catalyst by the batch reaction”.
If an alkylene oxide is continuously supplied without the batch reaction, which is a step of activating the polymerization activity of the catalyst, polymerization of the alkylene oxide does not proceed. As a result, a large amount of the alkylene oxide remains unreacted and accumulates in the reactor. As is acknowledged, the concentration of the alkylene oxide strongly influences activation of the polymerization activity of the catalyst. The reactor in which the alkylene oxide has accumulated to a high concentration is in danger of rapid progress of the reaction, that is, explosive polymerization of a large amount of the alkylene oxide. The explosive polymerization of a large amount of the alkylene oxide rapidly generates heat, which is accompanied with an increase in the internal temperature. The temperature increase in turn increases the vapor pressure of the alkylene oxide, and these factors may lead to a rapid increase in the internal pressure in a reactor and thus to troubles such as breakage of the reactor.
However, once being activated, the double metal cyanide complex catalyst enables smooth polymerization and smooth consumption of the alkylene oxide continuously supplied after the activation. In this case, dangerous excessive accumulation of the alkylene oxide is avoidable. Accordingly, when a double metal cyanide complex catalyst is used for the production of polyalkylene oxides, it is important, for the safety reason, to activate the double metal cyanide complex catalyst by the batch reaction and induce the polymerization activity before continuous supply of an alkylene oxide. However, low molecular weight initiators cause some problems. For example, the use of a low molecular weight initiator does not allow the batch reaction to proceed, or allows the batch reaction to proceed but at a remarkably slow rate and requires a longer time for activation of the catalyst by the batch reaction. To overcome the problems, a technique has been developed in which a mixed initiator including a first initiator having a comparatively low molecular weight and a second initiator having a comparatively high molecular weight is used so that the initiator having a low molecular weight is allowed to react (see Patent Document 3). Another technique has also been disclosed in which a first initiator having a comparatively high molecular weight is reacted with an alkylene oxide to yield an activated initiator in advance, a mixed initiator is prepared by mixing a second initiator having a comparatively low molecular weight with the activated initiator, and the mixed initiator is used so that the initiator having a low molecular weight is allowed to react (see Patent Document 4). In these techniques of producing polyalkylene oxides, the reactions may be carried out in an organic solvent such as tetrahydrofuran, as are described in, for example, Patent Documents 3, 4, and 5. However, no previous studies have provided sufficient data to discuss effects of the amount of an organic solvent on activation of the catalyst by the batch reaction when only a low molecular weight initiator is used for the production of polyalkylene oxides.    Patent Document 1: JP-A H03-72527    Patent Document 2: JP-A H03-47825    Patent Document 3: JP-A H04-59825    Patent Document 4: JP-A 2004-51996    Patent Document 5: JP-A H02-265903